1. Field of the Invention
The present invention relates to an image display apparatus and a control method therefor.
2. Description of the Related Art
In the past, in an image display apparatus using a liquid crystal device, there has been a technology in which a backlight is divided into a plurality of blocks, so that the brightness of the backlight and the transmittance of a liquid crystal are controlled based on an image signal for each block. As a result of this, the black floating (misadjusted black level) of a dark portion of an image is suppressed, and contrast is improved (for example, Japanese patent No. 3523170). Medical images represented by those taken by Roentgen or X rays, etc., are images in each of which a bright diagnostic image is disposed in a dark background, and in cases where such imaged are displayed by a liquid crystal display device, misadjusted black level may be visually recognized as disturbance. Accordingly, the disturbance of the black floating can be improved by reducing the backlight brightness of the dark portion of the image, by using the technology of the Japanese patent No. 3523170.
In addition, it is known that when the brightness of the backlight is changed rapidly, a flicker occurs, and so, there has been proposed a technology of alleviating a change in brightness of the backlight in order to reduce the flicker (for example, Japanese patent laid-open publication No. 2009-181075).